The present invention relates generally to a gas bearing of the dynamic pressure type and more particularly to a bearing wherein a rotary shaft is supported by an air layer under pressure formed between the shaft and a plurality of circumferentially disposed bearing pads.
Prior art gas bearings of the dynamic pressure type are constructed with a plurality of bearing pads equidistantly spaced about a rotary shaft supported by the bearing. Usually, at least three pads are provided with each pad having an arcuate sectional profile. Each of the pads is mounted upon a pivotal support member disposed toward the leading edge of the pad taken relative to the direction of rotation of the shaft. As a result, the rotation of the shaft operates to create a so-called "wedge action" which establishes an air film within the clearance between each of the pads and the shaft. As a result, the shaft is smoothly supported during its rotative movement.
Some of the pads are arranged to receive the load of the shaft with one of the pads being arranged so that it does not receive the load of the shaft. The pads which receive the shaft load, hereinafter referred to as load-bearing pads, are supported by pivots which are fixed to stationary supports. The remaining pad which does not receive the shaft load, hereinafter referred to as the non-load bearing pad, is supported by a pivot which is attached to a stationary support through a resilient interconnecting arm.
In a case where the rotary shaft is supported in a horizontal position, it therefore occurs that at a low rotational speed of the shaft the non load-bearing pad tends to drop or become displaced by the force of its own weight thereby coming into contact with the shaft. This usually occurs where a low level of air pressure is developed in the clearance between the pad and the shaft. Under such circumstances, the pad cannot be held in a stable position and it becomes susceptible to dislocation as a result of disturbances created in the bearing assembly. As a result, noise will be produced due to irregular contact of a portion of the dislocated pad with the shaft. Moreover, the pad will become subject to wear which tends to consequently shorten service life of the entire gas bearing assembly. Particularly, since the pad is supported by a pivotal mounting positioned toward its leading edge taken relative to the direction of rotation of the shaft, its trailing edge is more likely to come into contact with the rotation shaft because of the positional instability of the pad.
The present invention is aimed at providing an improvement in a gas bearing assembly whereby smooth rotational characteristics of the rotary shaft may be enhanced by eliminating the tendency of interference between a pad and the shaft even at low rotational speeds of the shaft.
The structure of the invention provides means whereby the pad which is not receiving the load of the shaft will be biased by a spring force directed radially inwardly of the shaft at the leading edge of the pad taken with respect to the direction of rotation of the shaft.